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M2 | Microbiolgy > Bacterial Dysentery > Flashcards

Bacterial Dysentery Flashcards

1
Q

How Enterohemorrhagic Escherichia coli is transmitted ?

A
  1. Ingestion of undercooked meat 🥩
  2. Direct contact with animals (Main reservoir is cattle)
  3. Ingestion of undercooked hamburger at fast-food restaurants ——-> Associated with outbreaks of bloody diarrhea
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2
Q

Pathogenesis of Enterohemorrhagic E.coli bloody diarrhea

A
  • Dysentery-like syndrome characterized by bloody diarrhea

* abdominal cramping & fever (similar to Shigella) —-> by producing “Shiga toxin” or “verotoxin” ( endotoxin )

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3
Q

What is the mechanism of shiga toxin ?

A

acts by removing adenine from large (28S) ribosomal RNA, thereby stopping protein synthesis

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4
Q

Pathogenesis of HUS in EE.coli

A

HUS ——> Hemolytic–uremic syndrome

  • complication consists of hemolytic anemia, thrombocytopenia & acute renal failure
  • Endothelium of small blood vessels & kidney epithelium has Shiga toxin receptors
  1. Death of kidney epithelial cells ——> renal failure
  2. Death of small blood vessels endothelial cells—> hemolytic anemia (red cells passing through damaged area become distorted (schistocytes) & lyse
  3. Thrombocytopenia (platelets adhere to damaged endothelium)
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5
Q

Enteroinvasive Escherichia coli (EIEC) invades the epithelium of which organ ?

A

Large intestine

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6
Q

EIEC causes bloody diarrhea (dysentery) accompanied by ___________ in stool.

A

inflammatory cells (neutrophils)

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7
Q

How to diagnose Enterohemorrhagic E.coli ?

A

cultured on Sorbitol MacConkey’s agar does not ferment sorbitol (distinguishes it from other strains of E. coli)

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8
Q

Important properties of salmonella

A
  • Gram-negative rods

* do not ferment lactose & produce H2S

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9
Q

State the antigens of salmonella

A
  1. “O” antigens: Outer polysaccharides of cell wall

2- ”H “ antigens: Flagellar antigens

3- “Vi” antigens: Capsular polysaccharides

  • Antiphagocytic (important virulence factor for S. typhi)
  • Serotyping of S. typhi in clinical laboratory
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10
Q

Mode of Transmission in salmonella

A

Ingestion of food & water contaminated by human & animal wastes

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11
Q

How human’s are a source of salmonella infection?

A
  1. Persons excrete organism during or shortly after attack of enterocolitis
  2. Chronic carriers: excrete organism for years
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12
Q

How animals are a source of salmonella infection?

A
  1. Poultry, eggs & undercooked meat

2. Dogs & other pets

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13
Q

Which type of salmonella is transmitted only in humans ?

A

S. typhi ( typhoid fever )

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14
Q

How Enterocolitis occur ?

A
  1. Invasion of epithelial & subepithelial tissue of small & large intestines inflammation & diarrhea
  2. Enterocolitis with nausea & vomiting then abdominal pain & diarrhea
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15
Q

What is the infectous dose of salmonella?

A

at least 100,000 organisms

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16
Q

What lowers the salmonella’s infectous dose?

A

Gastrectomy or use of antacids

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17
Q

What happens to HIV-infected individuals with salmonella infection?

A

They have low CD4 count ———> Salmonella infections

  • severe diarrhea
  • serious metastatic infections
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18
Q

What is the incubation period of Enterocolitis in salmonella?

A

12 to 48 hours

19
Q

Pathogenesis of Typhoid fever (S. typhi)& Enteric fever (S. paratyphi A, B & C)

A
  1. Organisms enter & multiply in mononuclear phagocytes of Peyer’s patches of small intestine ——-> phagocytes of liver, gallbladder & spleen ——> bacteremia & fever caused by endotoxin
  2. Salmonella invades gallbladder ———> carrier state & excretion of bacteria in feces for long periods
    * Salmonella survive within phagosomes in phagocytic cells
20
Q

What is the clinical findings of Typhoid fever (S. typhi)& Enteric fever (S. paratyphi A, B & C)?

A
  1. Fever & constipation rather than vomiting & diarrhea
  2. Diarrhea occur early but disappears & fever & bacteremia occur
  3. After 1st week ——> high fever, delirium, tender abdomen & enlarged spleen occur
  4. Rose spots (rose-colored macules on abdomen)
  5. Leukopenia & anemia
  6. Abnormal liver function ——-> hepatic involvement
  7. Severe complications : intestinal hemorrhage or perforation
21
Q

Pathogenesis of Septicemia (S. choleraesuis)

A
  1. Bacteremia ——-> osteomyelitis (child with sickle cell anemia) , pneumonia & meningitis
  2. Infarcts & aneurysms are most sites of metastatic abscesses
  3. Vascular graft infections
    * Fever but little or no enterocolitis
22
Q

Laboratory diagnosis of Enterocolitis

A

Salmonella is isolated from stool sample

23
Q

Laboratory diagnosis of enteric fever

A
  1. Blood culture : first 2 weeks of illness
  2. Bone marrow cultures : positive
  3. Stool cultures positive in chronic carriers (Salmonella is secreted in

bile into intestinal tract)

  1. Slide agglutination test:
    * Salmonella serogroup based on its O antigen
    * Serotyping of O, H & Vi antigens for epidemiology
  2. Serologically (Widal test):
    * detecting rise in antibody titer in patient’s serum in enteric fever
    * sepsis when organism is difficult to recover
24
Q

What does salmonella form in MacConkey’s agar/ EMB agar ?

A

non-lactose-fermenting (colorless) colonies

25
Q

How to diagnose salmonella in TSI agar ?

A

alkaline slant & acid butt with both gas & H2S

26
Q

S. typhi : does not form____ & produces only small amount of _____

A

Doesn’t form gas

Only small amount of H2S

27
Q

Important properties of Shigellae

A
  • non–lactose-fermenting
  • gram-negative rods
  • produce no gas from fermentation of glucose
  • do not produce H2S
  • non motile
  • All shigellae have O antigens (polysaccharide) in their cell walls
28
Q

What is the mode of transmission in shigellae ?

A
  • Shigellosis is only human disease
  • Fecal–oral route
  • No prolonged carrier state
29
Q

What is the infectious dose of shigellae ?

A

Very low infectious dose; ingestion of 100 organisms cause disease

30
Q

Clinical findings of shigellae

A
  1. Bloody diarrhea (Bacillary dysentery) :
    * by invasion of colonic microfold cells (critical factor)
  2. Some strains produce enterotoxin (Shiga toxin)
  3. Local inflammation accompanied by ulceration
  4. Fever & abdominal cramps followed by diarrhea with blood & mucus
31
Q

Incubation period of shigellae

A

1 to 4 days

32
Q

How shigellae is identified in MacConkey’s agar ?

A

non–lactose-fermenting (colorless) colonies

33
Q

How shigella appear in TSI agar ?

A

alkaline slant & acid butt, with no gas & no H2S

34
Q

Important properties of Campylobacter jejuni

A
  • Curved, comma- or S shaped gram-negative rods

* Microaerophilic, growing best in 5% oxygen at 42°C

35
Q

Transmission of C.jejuni

A
  • Fecal–oral
36
Q

What are the human sources causing C.jejuni infection?

A
  1. Domestic animals: cattle, chickens & dogs
  2. Foods: chicken, meat, unpasteurized milk & water contaminated with animal feces
  3. Human-to-human transmission occurs
37
Q

Clinical findings of C.jejuni

A
  1. Inflammation of intestinal mucosa
  2. Enterocolitis begins as
    * watery, foul-smelling diarrhea
    * followed by bloody stools with fever & severe abdominal pain
  3. Bacteremia:
    * in neonates or debilitated adults
38
Q

C.jejuni is associated with which syndrome and explain its pathogenesis?

A

Guillain-Barré syndrome (acute neuromuscular paralysis)

——> It is an autoimmune disease due to formation of antibodies against C. jejuni that cross-react with antigens on neurons

39
Q

Laboratory diagnosis of C.jejuni

A
  1. Diarrheal stool specimen:
    * cultured on blood agar plate containing antibiotics that inhibit other fecal flora
  2. Incubated at 42°C in microaerophilic atmosphere containing 5% oxygen & 10% carbon dioxide
  3. Failure to grow at 25°C
  4. Oxidase positivity
  5. Sensitivity to nalidixic acid
  6. Blood culture (bacteremia):
    * growth of comma- or S-shaped, motile, gram-negative rods
40
Q

Important properties & transmission of Yersinia enterocolitica

A
  • Gram-negative rods
  • Transmission:
    1. fecal contamination of food; raw pork (most commonly)
    2. unpasteurized milk products
    3. unfiltered water
41
Q

Pathogenesis of Yersinia enterocolitica

A
  • Enterocolitis (similar to Shigella & Salmonella)
  • Mesenteric adenitis (mimic appendicitis): inflammation of the lymph nodes in the abdomen
  • Rarely, bacteremia or abscesses of liver or spleen, in persons with
    underlying disease
42
Q

How Y. enterocolitica appear in stool culture?

A

lactose negative colony on MacConkey’s agar

43
Q

What is the Cold enrichment technique ?

A

stool sample incubation at 4°C for 1 week increases recovery of organism

44
Q

At which degree the Y. enterocolitica grows ?

A

Grows better at 25°C than at 37°C

M2 | Microbiolgy (17 decks)

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